A pixel of an OLED display is a light emitting diode constituted of a stacked structure. In a color pixel structure constituted of a red (R) sub-pixel, a green (G) sub-pixel and a blue (B) sub-pixel, positions and shapes of light emitting layers (EMLs) of sub-pixels in different colors should respectively correspond to electrodes (generally anodes, hereafter referred to as “sub-pixel electrodes”) of sub-pixels in different colors, in addition, the lower structure and the upper structure of the EMLs are common layers of the (sub) pixels in different colors. The light emitting layers of sub-pixels in different colors are made of different materials and have different vapor deposition target regions and patterns, thus they should be vapor deposited respectively. If material of EML of a sub-pixel in one color is deposited on a region of a sub-pixel electrode corresponding to another color, color mixing will be caused.
In order to limit deposition region of scattering particles during a vapor deposition process so as to form a light emitting layer with a predefined pattern at a specific position, the mainstream technology currently used in the industry is that, a fine metal mask (FMM) is located close to a substrate to prevent undesired particles from being deposited on regions of the substrate except for regions corresponding to holes of the FMM during a vapor deposition process. The holes of the FMM are aligned with sub-pixel electrode regions to be vapor deposited. Particles of organic electroluminescent material may be deposited on the sub-pixel electrode regions to form light emitting layers in shapes similar to that of the holes of the FMM. Different materials will be deposited by moving the FMM or using different FMMs to form desired organic light emitting layers of sub-pixel electrodes in different colors respectively.
However, the inventor found that there are following technical problems in technical solutions of the prior art, in which vapor deposition processes are performed by using the FMM(s). First, the FMM may be deformed due to gravity of deposited material and variation of temperature for vapor deposition, so that precision of positions and patterns of the light emitting layers formed by vapor depositing may be affected. Secondly, since shield function of the FMM, only a little of EML material will be deposited as the light emitting layer through the FMM, and other material will be deposited on the FMM so as to be wasted.